[time-nuts] Mercury Ion Clock

Jim Lux jimlux at earthlink.net
Sat Nov 1 14:35:29 EDT 2014

On 11/1/14, 11:05 AM, Magnus Danielson wrote:
> Jim,
>> However, if you were happy with "lab grade" construction, and you have
>> the Kurt Lesker and Duniway catalogs as bedside reading, I think you'd
>> have a chance.
> Yes. I guess a bit of baking out the build is also to be recommended.
> I guess most of us don't do vacuum in our labs, so there is a challenge
> in itself, as there is many beginners mistakes to be done there.

I haven't done high vacuum in quite a few years, but it is fascinating 
and frustrating. These days, quite a bit of surplus gear is out there 
that does make life easier (e.g. turbo molecular pumps).  A Hg Ion 
system isn't real huge, and doesn't have a big gas load, so a 
straightforward LN2 sorption pump would probably work as a batch 
mode(e.g. a bunch of the right material, plunged into a LN bath, and it 
the gas molecules just stick right to the material.. )

>> The ion trap and such is a fairly straightforward thing, from what I
>> understand: you need the usual vacuum pumps and such to build one.  If
>> you don't want it to run for years without servicing, then issues of the
>> mercury content are less important.
>> (BTW, the space clock uses thermal dissociation of HgO to get the
>> mercury)
> Have tou cared to get the right isotope or do you use the natural
> abundance spreading? Hg-199 has an abundance of 16,87%.

Interesting, I don't know if they go out and sort it, or if they set up 
the system so that it's basically a mass spec, and the wrong isotope 
doesn't make it through the quadrupole filter.  I'll bet the latter. No 
matter how good your offline enrichment process is, there will always be 
some other "stuff" in there.   For all I know, the actual ion trap is 
specific to the mass of the ions.

>> The PMT is an off the shelf thing. Check out the amateur built fusion
>> reactor (fusor) websites on where to get PMTs and amplifiers (they're
>> used behind a scintillator)
> Ah yes. Got a NaI(Tl) scintilator with about 1 cm copper filter and a
> matching PMT. No amp thought, but then again, I do not know what I
> should measure with it. :)

You can measure radiation from common household objects like bananas

>> The 40 GHz stuff these days is not nearly as exotic as it used to be.
>> The challenge might be test equipment when you're debugging your 40 GHz
>> synthesis chain.
> I was thinking the same, especially when consider optical clocks, then
> 40 GHz isn't as esoteric. Traditional cesiums and rubidiums use a pair
> of synthesized frequencies being then sent into a step-recover diode
> inside a tuned cavity which then does the mixing and selects the right
> combination.

Same scheme might work here. Next time I'm talking to one of the DSAC 
folks, I'll ask how they do the synthesis chain.

>> I don't think it would be *easy*, but I think doable, and nothing in the
>> system is particularly expensive or that exotic.  It's sort of like
>> telescope building.. The raw materials to make a 18" reflector telescope
>> aren't all that expensive, nor is there some secret sauce: it's just
>> time to grind the mirror (and recover from mistakes) and build the
>> system.
> Would be a fun project to do, things to be learned.

For when you get tired of counting femtoseconds..

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